Instructions for Installing Pet Doors

Measure your pet, both his width and height. Buy a pet door that is at least 2 inches wider than the widest part of your animal, and at least 2 inches taller than the height of your pet from the top of the shoulders to the bottom of the chest.

Use the template that comes with the pet door, or the plastic slide for the door, to mark where the pet door will be inserted. Place the template onto the door, keeping in mind that the bottom needs to be at least 3 inches above the bottom of the door, and trace it with a pencil.

Make an "X" mark on the inside of each corner.

Drill a hole in the center of each "X" using a 1/2-inch drill bit. If your template requires you to drill screw holes for the frame of the pet door, drill the holes in the appropriate location with a 3/8-inch drill bit.

Cut along the lines marked for the door with a jig saw. Begin in one of the drilled holes, and cut carefully along the pencil line.

Attach the outer frame to the exterior of the door. If the frame extends into the interior of the hole, use pliers to remove a break-off level -- horizontal and vertical pieces along the back of the frame that are meant to be removed and make the frame thinner. Continue to remove break-off levels until the outer frame is flush with the door. Screw in the frame, when applicable.

Insert the inner frame on the interior side of the door. The interior side of the frame will hold the plastic flap. Attach the frame per the manufacturer's instructions, probably by using screws.